Printing element and process of making same



Dec. 4, 1934.V B. L. SITES 1,982,967

PRINTING ELEMENT AND PROCESS 0F MAKING' SAME Filed oct. 9, 1951 PatentednDec. 4, 1934 UNITED STATES PRINTING ELEMENT AND PROCESS F MAKING SAMEBenjamin L. Sites, Chicago, Ill., assignor to The Miehle Printing Press& Mfg. Company, Chicago, Ill., a corporation of Illinois ApplicationOctober 9,

Claims.

My invention pertains to printing surfaces and more specically relatesto a process of producing printing elements such as are used in rotov 0is to say, the deep tones of a print will be produced by those cellswhich carry most ink, while the lighter tones are represented by theshallow, less ink carrying cells.

Heretofore intaglio printing surfaces were prof duced by the delicateand cumbersome carbon tissue method according to which method a carbontissue, such as regular commercial carbon paper, after it has beensensitized, is exposed through a screen and through a photographictransparency. The exposed tissue is then squeegeed onto a carefullyprepared base such as a sheet of copper, whereupon the base is subjectedto a dissolution treatment and etching process as is well known in theart.

The principal object of my invention is to eliminate the use of carbontissue and to thereby very substantially simplify the old methods ofproducing intaglio printing elements.

According to my invention, it will also be possible to correct errorsthat might occur during the preparation of a printing element, or tochange designs by retaining the same base, a feature which it wasimpossible to accomplish heretofore. In order to attain these and otherobjects which will become apparent from the following description andappended claims, I conceived a scheme of providing the surface of aprinting elementwith ink carrying cells which are all of the same, orapproximately the same, depth, and to then determine the in k carryingcapacity of the cells by applying thereto a material different' fromthat of which the base itself is made, preferably a photographicemulsion which, after having been exposed and developed, will leave inthe cells deposits of unequal depth corresponding to the various colortones required.

According to my invention I propose to proceed for example by flowing aprinting base such as a sheet of copper or a copper cylinder with a lmof bichromated gelatin or bichromated albumen, generally termedbichromated colloid, which film I subsequently expose through arotogravure screen and then develop it with warm water in thev usualmanner, so that a screen image will remain on the base. Preferably thedeveloped screen image is then baked so as to form a permanent resist.Thereupon I etch the base with ferric chloride which will produce ink1931, Serial N0. 567,776

retaining cells, all of which are of approximately the same depth.

It will be readily understood that instead of providing the screen imageon the printing base by the etching method as explained above, the sameresult could be accomplished mechanically such as by impressing `orrolling a screen image into the surface of the base. If produced in thismanner, the walls of the cells become hardened by the physical contactof the tool used for this purpose.

This would afford a decided advantage over the etching process becausethereby the surface of the printing element will be rendered moreresistant to the wear of the doctor blade which is generally used. forscraping the surplus ink off the printing surface of the element priorto effecting the impression.

The cells of the screen image are then flowed with a silver bromidegelatin photographic emulsion in a dark room and squeegeed off so thatthe emulsion will remain in the cells only. 'I'his emulsion will then beshrunk and thus solidified by dryingor by any other practical method sothat eventually its level will be below the plane of the screen image.

After this silver bromide gelatin emulsion is shrunk i. e. solidied, Iexpose it through a design carrying-transparency such as'by contact in avacuum frame, which exposure requires but a few seconds.

After exposure the emulsion in the cells of the copper plate orthe likewill be developed by any desired method, for instance in a photographicdeveloper so that the emulsion remaining in the cells will be of varyingthickness in proportion to the exposure received, and after developingthe emulsion which remains in the cells will be swelled either with analkaline or an acid solution. I have found that the swelled condition ofthe silver bromide gelatin emulsion can be rendered permanent byimmersing the `plate i. e. exposed surface into` a solution of alcohol,alum and formaline. drying of the surface by heat will cause the swelledemulsion to 'become hardened. By this swelling process the emulsion inthose cells which correspond with the high lights ofthe sibject, willcompletely fill said cells, so that no ink retaining depth will beprovided in these cells.

Another method whereby the swelling of the emulsion can be arrested i.e. rendered per. manent is that of saturating the swelled emulsion witha solution of sodium silicate and subsequently precipitating silica inthe gelatin with acid; or, saturating the swelled emulsion i. e. gelatinwith a solution of a salt and subsequently.

precipitating an insoluble compound by the addition of a precipitatingagent.

In Figures 1 to 9 of the accompanying draw- Subsequent ing, I haveillustrated one manner of carrying coating 11 of bichromated gelatin orbichromated albumen, see Figure 2, whereupon thiscoating 11 is exposedthrough a rotogravure screen 12 having transparent portions 13, seeFigure 3.

Figure 4 illustrates the printing element after it has been exposedthrough a screen; the portions 14 representing the exposed areas Whilethe portions 15 show the unexposed areas, which corresponded with theopaque sections of the screen and whichduring the development processwill dissolve so that the exposed portions 14 only remain on the base,such as is shown in Figure 5.

After developing, the plate will then be subjected to the) etchingprocess during which the ink carrying cells 16, see Figure 6, wilL beformed. These cells, as explained above, will all be of the same, orapproximately the same depth and will then be flowed with a silveremulsion such as a silver bromide gelatin photographic emulsion 17, seeFigure '7. lThis emulsion, after having been thoroughly dried and thussolidied, will then be exposed -through a photographic transparency 18,Figure 8, and then developed and swelled as explained above, whereby thehigh lights i. e. light tones willbe represented by the areas 19, whichcarry little or no ink at all, whereas the deeper tones will berepresented by the more vink carrying cells 20 as shown in Figure 9.

While I prefer to etch all the cells of the screen image to an evendepth, it is not essential to devote much care to that part of theprocess,

i because the ink retaining capacity of each cell is determined by theemulsion as explained', and

therefore minor variations in the depth of these i rotogravure printingelements will oler the following principal advantages:

s 1. The use of carbon tissue will be entirely dispensed with. l

2. Errors may be readily corrected, or new designs applied, by washingout the emulsion in the ink carrying cells and by repeating the flowingof the cells with emulsion and subsequently exposing and developing.This does not destroy the copper cells.

3. The etching of the base does not require the usual skill since aslight variation in thedepth of th cells produced does not result in anydefect in the nished plate.

4..,The swelling action of the gelatin can be controlled with less skillthan is now required for etching through carbon tissue.

5. The exposure of a plate can be readily accomplished in a step andrepeat machine, thereby attaining perfect register for multicolor work.

As an alternative, that is to say, .instead of flowing the ink carryingcells by a silver emulsion and then swelling that emulsion ashereinabove described, I find that equally satisfactory results can beobtained by owing said cells with bichromated gelatin, in which case,however, the

cells would have 'co remain filled, that is to say.,1 the gelatin vinthe cells must not be below the' plane of the printing element i. e.screenlimage when the gelatin is dry i. e. solidified'and at thevAccording to this scheme, instead of the emull swelling and drying theemulsion in said cells.

sion in the cells becoming swelled as explained above, those portions ofthe screen image which during the exposure through the photographictransparency were not exposed to the light will Qdissolve and wash outso that a printing element identical to that illustrated in Figure 9will be produced.

It is therefore my intention to cover any such modifications intheprocess of making printing elements that will come within the scope andessence of the appended claims.

` 1. The process of making intaglio printing elements, consisting inflowing a metal base with a light sensitive coating capable ofproducing`an etching resist, exposing. said coating through a screen,developing said coating, drying the screen image remaining on said base,-etching said base to provide ink retaining cells therein, applying aphotographic emulsionto said cells, drying said emulsion, exposing saidemulsion through a photographic transparency, developing the exposedemulsion to produce varying thickness in said cells in proportion to theexposure received, and drying the emulsion in said cells.

. 2. The process of making intaglio printing elements, consisting inowing a metal base-with a .stantially uniform depth therein, applying aphotographic emulsion to said'oells, drying said emulsion, exposing saidemulsion through a photographic transparency, developing the exposed,emulsionl to produce varying thickness in said cells in proportion tothe exposure received, and

3. The process of making intaglio printing elements, consisting inflowing a metal base with a light sensitive coating capable of producingan etching resist, exposing said coating through a screen, developingsaid coating, drying and baking the "creen image remaining on said base,etching id base to provide ink retaining cells therein, applying aphotographic emulsion to said cells, drying and-shrinking said emulsion,exposing said emulsion through a photographic transparency, developingthe exposed emulsion to produce varying thickness in said cells inproportion to the exposure. received, and swelling and dryingtheemulsion in said cells.

4. The process of making intaglio printing elements, consistinginproviding a metal base with ink retaining `cells of substantiallyuniform depth, applying a photographic emulsion to said cells, dryingsaid emulsion, exposing said emulsion through a photographictransparency, developing the exposed emulsion to produce varyingthickness in said cells in proportion to the.

exposure received, and swelling and drying the emulsion in said cells.

5. Thprocess of making intaglio printing elements, consisting inproviding a metal base with ink retaining cells of substantially uniformdepth, applying a photographic emulsion to said cells, drying andshrinking said emulsion, exposing said emulsion through a photographictransparency, developing the exposed emulsion to produce varyingthickness in said cells in" proportion to the exposure received, andswelling and drying the-emulsion in said cells.

BENJAMIN L. SITES.

.light sensitive coating capable of producing an

